A NEW NUMERICAL-MODEL OF THE MIDDLE ATMOSPHERE .2. OZONE AND RELATED SPECIES

A new two-dimensional model with detailed photochemistry is presented. The model includes descriptions of planetary wave and gravity wave pr opagation and dissipation to characterize the wave forcing and associa ted mixing in the stratosphere and mesosphere. Such a representation a llows for explicit calculation of the regions of strong mixing in the middle atmosphere required for accurate simulation of trace gas transp ort. The new model also includes a detailed description of photochemic al processes in the stratosphere and mesosphere. The downward transpor t of H-2, H2O, and NO(y) from the mesosphere to the stratosphere is ex amined, and it is shown that mesospheric processes can influence the d istributions of these chemical species in polar regions. For HNO3 we a lso find that small concentrations of liquid aerosols above 30 km coul d play a major role in determining the abundance in polar winter at hi gh latitudes. The model is also used to examine the chemical budget of ozone in the midlatitude stratosphere and to set constraints on the e ffectiveness of bromine relative to chlorine for ozone loss and the ro le of the HO2 + BrO reaction. Recent laboratory data used in this mode ling study suggest that this process greatly enhances the effectivenes s of bromine for ozone destruction, making bromine-catalyzed chemistry second only to HO(x)-catalyzed ozone destruction in the contemporary stratosphere at midlatitudes below about 18 km. The calculated vertica l distribution of ozone in the lower stratosphere agrees well with obs ervations, as does the total column ozone during most seasons and lati tudes, with the important exception of southern hemisphere winter and spring.